Many who think they have a peni­cillin al­lergy are mis­taken

The Irish Times - Tuesday - Health - - Lifestyle - Muiris Hous­ton mhous­ton@irish­times.com

“New medicines and new meth­ods of cure al­ways work mir­a­cles for a while.” – Wil­liam He­ber­den, an 18th­cen­tury Bri­tish physi­cian

Are you al­ler­gic to peni­cillin? It’s the most com­monly re­ported drug al­lergy in this part of the world, with one in 10 peo­ple say­ing they have an al­lergy to the an­tibi­otic.

How­ever, it has been es­ti­mated that just 10 to 20 per cent of those re­port­ing peni­cillin al­lergy are truly al­ler­gic. So what, you may ask?

Well it’s im­por­tant that the term “peni­cillin al­lergy” is cor­rectly ap­plied in or­der to avoid ad­verse ef­fects or in­ap­pro­pri­ate treat­ment. And in an era of an­tibi­otic re­sis­tance and few new drugs in the pipe­line, it makes sense to iden­tify those who are, in fact, not al­ler­gic to a very use­ful group of drugs.

We know that peo­ple with sus­pected but un­ver­i­fied peni­cillin al­lergy are likely to be treated with al­ter­na­tive an­tibac­te­ri­als that are more likely to con­trib­ute to mi­cro­bial re­sis­tance.

Alexan­der Flem­ing serendip­i­tously dis­cov­ered peni­cillin be­tween the two World Wars. By early 1944, the new mir­a­cle drug was widely avail­able, ini­tially for Al­lied troops and then the civil­ian pop­u­la­tion.

In­ter­est­ingly, re­search has shown that peo­ple with a his­tory of sus­pected peni­cillin al­lergy spend more time in hospi­tal and have poorer clin­i­cal out­comes than pa­tients with­out such a his­tory.

In­cor­rect la­belling

In a US study, those with a la­bel of peni­cillin al­lergy were ex­posed to sig­nif­i­cantly more an­tibi­otics such as flu­o­ro­quinolones, clin­damycin and van­comycin and had higher rates of Clostrid­ium dif­fi­cile, MRSA and van­comycin-re­sis­tant en­te­ro­coc­cus (VRE) in­fec­tions than their non-peni­cillin al­ler­gic peers.

And ev­i­dence is be­gin­ning to emerge that the re­moval of in­cor­rect la­belling of peni­cillin al­lergy can de­crease broad-spec­trum an­tibac­te­rial use and re­duce length of in­pa­tient stay, mor­tal­ity and treat­ment costs.

There are ba­si­cally two types of peni­cillin al­lergy based on the tim­ing of ap­pear­ance of symp­toms: im­me­di­ate or de­layed. Im­me­di­ate re­ac­tions have their on­set in one to six hours (usu­ally within 60 min­utes) af­ter ex­po­sure to a dose of an an­tibi­otic and of­ten in­volve ini­tial skin re­ac­tions such as ur­ticaria (hives) or itch­ing all the way to swelling of the throat and neck and full blown ana­phy­lac­tic shock.

De­layed or non-im­me­di­ate re­ac­tions usu­ally oc­cur sev­eral days af­ter ex­po­sure to peni­cillin and in­volve a dif­fer­ent type of im­mune sys­tem re­sponse. Typ­i­cally peo­ple no­tice ei­ther a flat red­dish skin rash or hives.

Is peni­cillin al­lergy more likely to af­fect cer­tain peo­ple? Women and older peo­ple are at higher risk; and there is a link be­tween fre­quent ex­po­sure to peni­cillin and the like­li­hood of an al­ler­gic re­ac­tion.

In a study of chil­dren, rang­ing in age from six months to 14.5 years, in whom de­layed-on­set skin rash af­ter peni­cillin ad­min­is­tra­tion had been re­ported, the rash re­curred in only seven per cent when they were re-ex­posed to peni­cillin. This may be ex­plained by its sim­i­lar­ity to the com­mon skin rash seen in vi­ral ill­ness in kids.

There are three steps needed to

Peo­ple with a his­tory of sus­pected peni­cillin al­lergy spend more time in hospi­tal and have poorer clin­i­cal out­comes than pa­tients with­out such a his­tory

ver­ify a di­ag­no­sis of peni­cillin al­lergy: a de­tailed clin­i­cal his­tory; skin test­ing; and in cer­tain cases an oral provo­ca­tion test where the per­son takes peni­cillin again orally. If both skin and oral tests are neg­a­tive, then they do not have a true peni­cillin al­lergy.

The in­ves­ti­gat­ing doc­tor will be es­pe­cially in­ter­ested in the route of ad­min­is­tra­tion of peni­cillin and whether the symp­toms of a pre­sumed re­ac­tion were im­me­di­ate or de­layed.

Skin test­ing should be car­ried out in a spe­cial­ist al­lergy cen­tre that is equipped to deal with a se­vere al­ler­gic re­sponse. For peo­ple with neg­a­tive skin test re­sults, an oral drug chal­lenge may be rec­om­mended. But it is not suit­able for any­one who has had a se­vere, life-threat­en­ing re­ac­tion to peni­cillin.

Vaguely aware you have a peni­cillin al­lergy? There’s an 80 per cent chance you have been in­cor­rectly la­belled.

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